Dynamo action generated by a precession driven flow in a cylindrical container


Dynamo action generated by a precession driven flow in a cylindrical container

Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.

Since many years precession is regarded as an alternative flow driving mechanism that may account, e.g., for remarkable features of the ancient lunar magnetic field or as a complementary power source for the geodynamo. Precessional forcing is also of great interest from the experimental point of view because it represents a natural forcing mechanism that allows an efficient driving of conducting fluid flows on the laboratory scale without making use of propellers or pumps. Within the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) a dynamo experiment is under development at Helmholtz-Zentrum Dresden-Rossendorf in which a precession driven flow of liquid sodium with a magnetic Reynolds number of up to Rm=700 will be used to drive dynamo action.

Our present study addresses preparative numerical simulations and flow measurements at a small model experiment running with water. In dependence of precession ratio and Reynolds number the resulting hydrodynamic flow patterns and amplitudes provide the essential ingredients for kinematic dynamo models that are used to estimate whether the particular flow is able to drive a dynamo. In the strongly non-linear regime the flow essentially consists of standing inertial waves. Most remarkable feature is the resonant-like occurrence of a stationary axisymmetric mode which emerges around a precession ratio Ωp/Ωc = 0.1. Kinematic dynamo models applying the time-averaged flow field from the hydrodynamic simulations exhibit dynamo action at a critical magnetic Reynolds number of Rmc=430 which is well within the range that will be achieved in the planned large scale sodium experiment.

Keywords: Dynamo; DRESDYN

  • Poster
    Dynamos and planetary flows today (PHR2017), 16.-17.11.2017, London, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-26124
Publ.-Id: 26124